A distributed file system is a system that manages data of files and the like by using a plurality of distributed storage devices (such as hard disk drives (HDDs), for example). The power consumed by a distributed file system may be reduced by stopping the supply of power to storage devices that are not in use.
For example, the following technique exists for power saving of a system including storage devices. Requests for input or output of data with respect to a data storage are stored as an access history, and whether an access will be requested with respect to the data storage at a predetermined timing is determined based on the access history. When it is determined that an access will not be requested, the supply of power to the data storage is stopped. When it is determined that an access will be requested, power is supplied to the data storage.
The following technique also exists. The order of past access actions to a storage system's logical volumes is recorded. The supply of power to a disk with the oldest access time is stopped, and a disk predicted to be accessed next is powered on.
Here, even if a disk is stopped based on access prediction by a method described above, the prediction might be wrong and the disk might be accessed. If so, the disk has to be rebooted. In this case, it takes time before the disk becomes accessible, and the power consumption may not be reduced either.
Related techniques are disclosed in, for example, Japanese Laid-open Patent Publication No. 2009-80603 and Japanese Laid-open Patent Publication No. 2008-112292.